Re: [PATCH v3] cgroup/freezer: add per freezer duty ratio control

From: Kirill A. Shutemov
Date: Mon Feb 07 2011 - 13:29:45 EST

On Mon, Feb 07, 2011 at 10:13:03AM -0800, jacob.jun.pan@xxxxxxxxxxxxxxx wrote:
> From: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
>
> Freezer subsystem is used to manage batch jobs which can start
> stop at the same time. However, sometime it is desirable to let
> the kernel manage the freezer state automatically with a given
> duty ratio.
> For example, if we want to reduce the time that backgroup apps
> are allowed to run we can put them into a freezer subsystem and
> set the kernel to turn them THAWED/FROZEN at given duty ratio.
>
> This patch introduces two file nodes under cgroup
> freezer.duty_ratio_pct and freezer.period_sec
>
> Usage example: set period to be 5 seconds and frozen duty ratio 90%
> [root@localhost aoa]# echo 90 > freezer.duty_ratio_pct
> [root@localhost aoa]# echo 5 > freezer.period_sec
>
> Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> ---
> Documentation/cgroups/freezer-subsystem.txt | 23 ++++++
> kernel/cgroup_freezer.c | 109 ++++++++++++++++++++++++++-
> 2 files changed, 130 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/cgroups/freezer-subsystem.txt b/Documentation/cgroups/freezer-subsystem.txt
> index 41f37fe..2bc1b98 100644
> --- a/Documentation/cgroups/freezer-subsystem.txt
> +++ b/Documentation/cgroups/freezer-subsystem.txt
> @@ -100,3 +100,26 @@ things happens:
> and returns EINVAL)
> 3) The tasks that blocked the cgroup from entering the "FROZEN"
> state disappear from the cgroup's set of tasks.
> +
> +In embedded systems, it is desirable to manage group of applications
> +for power saving. E.g. tasks that are not in the foreground may be
> +frozen unfrozen periodically to save power without affecting user
> +experience. In this case, user/management software can attach tasks
> +into freezer cgroup then specify duty ratio and period that the
> +managed tasks are allowed to run.
> +
> +Usage example:
> +Assuming freezer cgroup is already mounted, application being managed
> +are included the "tasks" file node of the given freezer cgroup.
> +To make the tasks frozen at 90% of the time every 5 seconds, do:
> +
> +[root@localhost ]# echo 90 > freezer.duty_ratio_pct
> +[root@localhost ]# echo 5 > freezer.period_sec
> +
> +After that, the application in this freezer cgroup will only be
> +allowed to run at the following pattern.
> + __ __ __
> + | |<-- 90% frozen -->| | | |
> +____| |__________________| |__________________| |_____
> +
> + |<---- 5 seconds ---->|
> diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
> index e7bebb7..928f2ab 100644
> --- a/kernel/cgroup_freezer.c
> +++ b/kernel/cgroup_freezer.c
> @@ -21,6 +21,7 @@
> #include <linux/uaccess.h>
> #include <linux/freezer.h>
> #include <linux/seq_file.h>
> +#include <linux/kthread.h>
>
> enum freezer_state {
> CGROUP_THAWED = 0,
> @@ -28,12 +29,23 @@ enum freezer_state {
> CGROUP_FROZEN,
> };
>
> +struct freezer_duty {
> + u32 ratio; /* percentage of time frozen */
> + u32 period_pct_ms; /* one percent of the period in miliseconds */
> +};
> +
> struct freezer {
> struct cgroup_subsys_state css;
> enum freezer_state state;
> + struct freezer_duty duty;
> + struct task_struct *fkh;
> spinlock_t lock; /* protects _writes_ to state */
> };
>
> +static struct task_struct *freezer_task;
> +static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer);
> +static void unfreeze_cgroup(struct cgroup *cgroup, struct freezer *freezer);
> +
> static inline struct freezer *cgroup_freezer(
> struct cgroup *cgroup)
> {
> @@ -63,6 +75,35 @@ int cgroup_freezing_or_frozen(struct task_struct *task)
> return result;
> }
>
> +static DECLARE_WAIT_QUEUE_HEAD(freezer_wait);
> +
> +static int freezer_kh(void *data)
> +{
> + struct cgroup *cgroup = (struct cgroup *)data;
> + struct freezer *freezer = cgroup_freezer(cgroup);
> +
> + do {
> + if (freezer->duty.ratio < 100 && freezer->duty.ratio >= 0 &&
> + freezer->duty.period_pct_ms) {
> + if (try_to_freeze_cgroup(cgroup, freezer))
> + pr_info("cannot freeze\n");
> + msleep(freezer->duty.period_pct_ms *
> + freezer->duty.ratio);
> + unfreeze_cgroup(cgroup, freezer);
> + msleep(freezer->duty.period_pct_ms *
> + (100 - freezer->duty.ratio));
> + } else if (freezer->duty.ratio == 100) {
> + if (try_to_freeze_cgroup(cgroup, freezer))
> + pr_info("cannot freeze\n");
> + sleep_on(&freezer_wait);
> + } else {
> + sleep_on(&freezer_wait);
> + pr_debug("freezer thread wake up\n");
> + }
> + } while (!kthread_should_stop());
> + return 0;
> +}
> +
> /*
> * cgroups_write_string() limits the size of freezer state strings to
> * CGROUP_LOCAL_BUFFER_SIZE
> @@ -150,7 +191,11 @@ static struct cgroup_subsys_state *freezer_create(struct cgroup_subsys *ss,
> static void freezer_destroy(struct cgroup_subsys *ss,
> struct cgroup *cgroup)
> {
> - kfree(cgroup_freezer(cgroup));
> + struct freezer *freezer;
> +
> + freezer = cgroup_freezer(cgroup);
> + kthread_stop(freezer->fkh);
> + kfree(freezer);
> }
>
> /*
> @@ -282,6 +327,16 @@ static int freezer_read(struct cgroup *cgroup, struct cftype *cft,
> return 0;
> }
>
> +static u64 freezer_read_duty_ratio(struct cgroup *cgroup, struct cftype *cft)
> +{
> + return cgroup_freezer(cgroup)->duty.ratio;
> +}
> +
> +static u64 freezer_read_period(struct cgroup *cgroup, struct cftype *cft)
> +{
> + return cgroup_freezer(cgroup)->duty.period_pct_ms / 10;
> +}
> +
> static int try_to_freeze_cgroup(struct cgroup *cgroup, struct freezer *freezer)
> {
> struct cgroup_iter it;
> @@ -368,19 +423,69 @@ static int freezer_write(struct cgroup *cgroup,
> return retval;
> }
>
> +static int freezer_write_duty_ratio(struct cgroup *cgroup, struct cftype *cft,
> + u64 val)
> +{
> + if (!cgroup_lock_live_group(cgroup))
> + return -ENODEV;
> + cgroup_freezer(cgroup)->duty.ratio = val;
> + cgroup_unlock();
> + wake_up(&freezer_wait);
> +
> + return 0;
> +}
> +
> +static int freezer_write_period(struct cgroup *cgroup, struct cftype *cft,
> + u64 val)
> +{
> + if (!cgroup_lock_live_group(cgroup))
> + return -ENODEV;
> + cgroup_freezer(cgroup)->duty.period_pct_ms = val * 10;

1 second == 1000 millisecond, I guess ;)

I think better to use milliseconds for the interface.

> + cgroup_unlock();
> + wake_up(&freezer_wait);
> +
> + return 0;
> +}
> +
> static struct cftype files[] = {
> {
> .name = "state",
> .read_seq_string = freezer_read,
> .write_string = freezer_write,
> },
> + {
> + .name = "duty_ratio_pct",
> + .read_u64 = freezer_read_duty_ratio,
> + .write_u64 = freezer_write_duty_ratio,
> + },
> + {
> + .name = "period_sec",
> + .read_u64 = freezer_read_period,
> + .write_u64 = freezer_write_period,
> + },
> +
> };
>
> +#define FREEZER_KH_PREFIX "freezer_"
> static int freezer_populate(struct cgroup_subsys *ss, struct cgroup *cgroup)
> {
> + int ret = 0;
> + char thread_name[32];
> + struct freezer *freezer;
> +
> if (!cgroup->parent)
> return 0;
> - return cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files));
> +
> + freezer = cgroup_freezer(cgroup);
> + ret = cgroup_add_files(cgroup, ss, files, ARRAY_SIZE(files));
> +
> + snprintf(thread_name, 32, "%s%s", FREEZER_KH_PREFIX,
> + cgroup->dentry->d_name.name);
> + freezer->fkh = kthread_run(freezer_kh, (void *)cgroup, thread_name);
> + if (IS_ERR(freezer_task))
> + pr_debug("%s failed to create %s\n", __func__, thread_name);
> +
> + return ret;

Hm.. I think it's waste of resources creates one threads for every cgroup.
In most cases auto freezing will not be enabled. Can we create a thread
when it's really needed (ratio != 0 && period != 0)?
Can we use delayed workqueues instead of separate thread?

> }
>
> struct cgroup_subsys freezer_subsys = {
> --
> 1.7.0.4
>

--
Kirill A. Shutemov
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